1. Field of the Invention
The invention relates to wear resistant lubricating oil formulations comprising a natural, synthetic or unconventional base oil or mixtures thereof, preferably a base stock derived from waxy feed, preferably waxy Fischer-Tropsch (F-T) hydrocarbons and containing an effective amount of one or more antiwear additives.
2. Related Art
Internal combustion engine lubricating oils require the presence of antiwear additives in order to provide adequate antiwear protection for the engine. Increasing specifications for engine oil performance have exhibited a trend for increasing antiwear properties of the oil. While there are many different types of antiwear additives, for several decades the principal antiwear additive for internal combustion engine crankcase oils has been a metal alkyl-thiophosphate and more particularly a metal dialkyldithiophosphate in which the primary metal constituent is zinc, or zinc dialkyldithiophosphate (ZDDP). The ZDDP is typically used in amounts of from about 0.7 to 1.4 wt % of the total lube oil composition. However, it has been found that the phosphorus from these additives has a deleterious effect on the catalyst in catalytic converters and also on oxygen sensors in automobiles. Furthermore, some antiwear additives add to engine deposits, which causes increased oil consumption and an increase in particulate and regulated gaseous emissions. Therefore, reducing the amount of metal dialkyldithiophosphate such as ZDDP in the oil without compromising wear performance would be desirable. OEMs are requiring low ash/reduced ash specifications for current and future light diesel vehicles. One solution to this problem is to use expensive supplementary, phosphorus-free antiwear additives as set forth, for example, in U.S. Pat. No. 4,764,294.
In U.S. Pat. No. 6,165,949 it is taught that premium lubricant oil formulations which exhibit enhanced antiwear properties comprise a base oil derived from a waxy F-T feedstock by the isomerization of such waxy feed and dewaxing the isomerate, to which is added an antiwear additive. The antiwear additives recited include a long list of such materials including metal phosphates, preferably metal dithiophosphates, metal thiocarbamates, metal dithiocarbamates and ashless antiwear additives exemplified by ethoxylated amine dialkyldithiophosphates and ethoxylated amine dithiobenzoates which are ionic. The preferred antiwear additive is identified as zinc dialkyldithiophosphate.
It would be an improvement to the art if the antiwear performance of a lubricating oil formulation could be improved beyond the levels currently achievable with the heretofore-disclosed and identified antiwear additive without resort to the use merely of greater quantities of such additives. Further, current and future specification for engine oils call for reduced ash in the oil for the next generation of vehicles.